Restrict verify_overlaps to pre S modules

The runtime in S and above does not have the same constraints that
require the hiddenapi flags to be generated in a monolithic manner.
This CL restricts the verify_overlaps to pre S modules. This will
filter out hiddenapi signature discrepancies that do not require
any action.

Test: verify_overlaps diff with this change https://diff.googleplex.com/#key=xxB0ky93hZRn
Test: presubmits
Bug: 313672880

Change-Id: Ie626a6779fc924563bec90b6c1ab0c7e8b4b23c2